Well he could get sheets of blue foam and cut them for insertion to the outside wall, but if the sheetrock is already up then spray is his only option.

The good about the blue sheets is they are something like R34 rated and are cheap and relativley easy to install (no brainer really). The bad is that if you get an electrical short in the wall which sparks off the foam then your walls will be burnt down faster than you could imagine so you have to make sure all of your electrical is completely up to par and not overloaded.